Oil additives, compositions and polymers for use therein

ABSTRACT

Compositions comprising an ethylene/vinyl acetate or propionate/vinyl linear carboxylate terpolymer improve the low temperature properties of oils having wax contents of at least 3% wt.

This invention relates to oil compositions, primarily to fuel oil compositions, and more especially to fuel oil compositions susceptible to wax formation at low temperatures, to copolymers for use with such fuel oil compositions, and to methods for their manufacture.

Fuel oils, whether derived from petroleum or from vegetable sources, contain components, e.g. alkanes, that at low temperature tend to precipitate as large crystals or spherulites of wax in such a way as to form a gel structure which causes the fuel to lose its ability to flow. The lowest temperature at which the fuel will still flow is known as the pour point.

As the temperature of the fuel falls and approaches the pour point, difficulties arise in transporting the fuel through lines and pumps. Further, the wax crystals tend to plug fuel lines, screens, and filters at temperatures above the pour point. These problems are well recognized in the art, and various additives have been proposed, many of which are in commercial use, for depressing the pour point of fuel oils. Similarly, other additives have been proposed and are in commercial use for reducing the size and changing the shape of the wax crystals that do form. Smaller size crystals are desirable since they are less likely to clog a filter. The wax from a diesel fuel, which is primarily an alkane wax, crystallizes as platelets; certain additives inhibit this and cause the wax to adopt an acicular habit, the resulting needles being more likely to pass through a filter than are platelets. The additives may also have the effect of retaining in suspension in the fuel the crystals that have formed, the resulting reduced settling also assisting in prevention of blockages.

Effective wax crystal modification (as measured by cold flow plugging point (CFPP) and other operability tests, as well as simulated and field performance) may be achieved by ethylene-vinyl acetate (EVAC) or propionate copolymer-based flow improvers.

In "Wissenschaft und Technik" 42(6), 238 (1989), M. Ratsch & M. Gebauer describe cold flow additives including an EVAC which has been hydrolysed and reesterified with, inter alia, propionic, n-pentanoic and n-hexanoic acids. A preference is expressed for esterifying acids to be straight-chain; a branched chain 3-methyl butanoic acid esterified copolymer gave significantly inferior results to those obtained using n-pentanoic acid esterified material.

In JP-A-58129096, cold flow additives comprising ethylene-vinyl carboxylic acid esters are described, the esterifying acid having a total carbon atom number of from 4 to 8, the additives being especially useful in a narrow boiling middle distillate fuel oil. The degree of branching of the main chain as measured by proton NMR is said to be at at least 6 alkyl branches per 100 methylene groups.

In WO 94/00536, cold flow additives comprising a terpolymer of ethylene and two different unsaturated esters are disclosed. Terpolymers are also described in EP-A-493769, the starting monomers being ethylene, vinyl acetate, and vinyl neo-nonanoate or -decanoate, and in the references cited in the search report on that application.

In British Specification No. 913715, ethylene-vinyl ester copolymers are proposed as pour point depressants for middle distillate fuels; as esterifying acids there are mentioned saturated aliphatic carboxylic acids containing from 4 to 10, 12, and 18 carbon atoms in their alkyl groups, the examples including n-octanoic acid.

British Specification No. 1,314,855 discloses terpolymers prepared from ethylene, vinyl acetate, and a vinyl ester of a long-chain carboxylic acid. Suitable long chain acids include C₈ -C₃₀ saturated carboxylic acids, for example lauric, myristic, palmitic and stearic acids. The terpolymers are described as useful viscosity index modifiers in lubricating oil compositions.

British Specification No. 1,244,512 discloses terpolymers of ethylene, a vinyl ester of a C₂ to C₄ mono-carboxylic acid and a copolymerisable unsaturated ester having C₁₀ to C₂₂ alkyl groups. The latter esters may, for example, be vinyl ester of a C₁₀ to C₂₂ monocarboxylic acid such as lauric, myristic, palmitic or stearic acid. The terpolymers are described as useful pour point depressants and filterability improvers for middle distillate fuel oils.

There exists a continuing need for additives showing improved performance over the prior art additives, in particular in oils having relatively high wax contents, for example above 3% by weight at 10° C. below cloud point. Such oils have hitherto often proved difficult to treat with conventional additives.

Surprisingly, we have now found that certain terpolymers having specific linearity (in the sense of the degree of alkyl branching from the main polymer chain) and preferably specific relative proportions of different monomers provide improved wax crystal modification to oils of relatively high wax content.

In a first aspect, the present invention provides an oil composition comprising an oil having a wax content of at least 3% by weight at 10° C. below its cloud point, and a flow improver composition comprising an oil-soluble ethylene terpolymer having, in addition to units derived from ethylene, units of the formula: ##STR1## and units of the formula ##STR2## wherein R¹ and R², which may be the same or different, each represent H or methyl, R³ represents an alkyl group containing up to 4 carbon atoms, and R⁴ represents a straight-chain alkyl group having from 3 to 15 carbon atoms, R³ and R⁴ being different; the degree of branching of the terpolymer, as measured by proton NMR spectroscopy (as explained in more detail below) being less than 6 CH₃ groups per 100 CH₂ units.

The term "terpolymer", as used herein, requires the polymer to have at least three different repeat units, i.e., be derivable from at least three different monomers, and includes polymers derivable from four or more monomers. For example, the polymer may contain two or more different units of the formula I or II, and/or may contain units of the formula ##STR3## wherein R⁵ represents a hydrocarbyl group having 3 or more carbon atoms other than one as defined by R⁴.

As used in this specification the term "hydrocarbyl" refers to a group having a carbon atom directly attached to the rest of the molecule and having a hydrocarbon or predominantly hydrocarbon character. Among these, there may be mentioned hydrocarbon groups, including aliphatic, (e.g., alkyl), alicyclic (e.g., cycloalkyl), aromatic, aliphatic and alicyclic-substituted aromatic, and aromatic-substituted aliphatic and alicyclic groups. Aliphatic groups are advantageously saturated. These groups may contain non-hydrocarbon substituents provided their presence does not alter the predominantly hydrocarbon character of the group. Examples include keto, halo, hydroxy, nitro, cyano, alkoxy and acyl. If the hydrocarbyl group is substituted, a single (mono) substituent is preferred. Examples of substituted hydrocarbyl groups include 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-ketopropyl, ethoxyethyl, and propoxypropyl. The groups may also or alternatively contain atoms other than carbon in a chain or ring otherwise composed of carbon atoms. Suitable hetero atoms include, for example, nitrogen, sulfur, and, preferably, oxygen. Advantageously, the hydrocarbyl group contains at most 30, preferably at most 15, more preferably at most 10 and most preferably at most 8, carbon atoms.

The terpolymer may also contain units of formulae other than those mentioned above, as may the copolymer, for example units of the formula

    --CH.sub.2 --CHR.sup.6 --                                  V

where R⁶ represents --OH, or of the formula

    --CCH.sub.3 (CH.sub.2 R.sup.7)--CHR.sup.8 --               VI

where R⁷ and R⁸ each independently represent hydrogen or an alkyl group with up to 4 carbon atoms, the units VI advantageously being derived from isobutylene, 2-methylbut-2-ene or 2-methylpent-2-ene.

In units of the formula I, R¹ advantageously represents hydrogen, and R³ advantageously represents ethyl or, more especially, methyl. In units of the formula II, R² advantageously represents hydrogen. R⁴ may represent propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, or tridecyl, and advantageously represents heptyl.

As indicated above, it is within the scope of the invention to provide a terpolymer containing a mixture of different species of R³ and/or R⁴. It is also within the scope of the invention to provide a composition containing two or more terpolymers.

The ester-containing units of the terpolymer, more especially the units of Formulae I and II, advantageously represent from 0.3 to 35 molar per cent of the terpolymer. The terpolymer is preferably of type (i), in which the ester groups advantageously constitute from 7.5 to 35 molar per cent, preferably from 10 to 25, and more preferably from 13 to 17, molar per cent. Advantageously units of the formula I represent from 1 to 4, preferably from 1 to 2, molar percent with units of the formula II representing from 12 to 15, preferably from 13 to 15, molar percent. Alternatively the terpolymer may be of type (ii) in which the ester groups advantageously represent up to 10, more advantageously from 0.3 to 7.5, and preferably from 3.5 to 7.0 molar per cent.

The terpolymer advantageously has a number average molecular weight, Mn, as measured by gel permeation chromatography, of at most 20,000. If the polymer is of type (i), its molecular weight is, generally, at most 14,000, advantageously at most 10,000, more advantageously in the range of 1,400 to 7,000, preferably 3,000 to 6,000 and most preferably from 3,500 to 5,500. If the polymer is of type (ii) the number average molecular weight is advantageously at most 20,000, preferably up to 15,000 and more preferably from 1,200 to 10,000, and most preferably from 3,000 to 10,000.

An important feature of the terpolymer according to the invention is its linearity, in the sense of the relatively small proportion of alkyl branches from the main polymer chain. This degree of branching may be expressed in terms of the number of methyl groups per 100 methylene units, as measured by proton NMR, which is, as indicated above, below 6, and advantageously within the range of from 1.0 to 4.5, more particularly 2.5 to 4.0, for example 2.6 to 3.6.

In calculating linearity, the proportion of CH₃ groups per 100 methylene groups is measured by proton NMR and corrected for the number of terminal methyl groups, based on the number average molecular weight, a relatively small correction, and, more importantly, for the number of methyl and methylene groups in the alkyl groups of R³ and R⁴ of the carboxylate side chains.

FIG. 1 shows a sample proton NMR spectrum for the ethylene-vinyl acetate vinyl-octanoate terpolymer of example 4, as hereinafter defined.

As shown in FIG. 1, the peaks relevant to the calculation are annotated b, c, d, and e, wherein b originates for the hydrogen(s) on the carbon atom situated α to the carbonyl group on the carboxylate side chain R4 (in this example, a methylene carbon); c represents the equivalent hydrogen(s) on R³ (in this example, methyl); d originates from the hydrogens of the methylenes and methines of the polymer main chain and carboxylate side chains, other than the main chain methines from which the carboxylate side chains depend where R¹ and/or R² in formula 1 represent H; and e originates from the hydrogens of the methyls of the polymer main chain and carboxylate side chains.

Representing the area under each of the peaks b, c, d and e as B, C, D, and E respectively, the number of CH₃ units per 100 methylene groups, corrected for carboxylate side chain methyl and methylene groups, is calculated as: ##EQU1## and this is then further corrected for the terminal methyl groups of the polymer chain by subtraction of the term ##EQU2## wherein Mole E represents the mole % of ethylene in the polymer, and x represents: ##EQU3## to give the degree of branching of the terpolymer.

The terpolymer may be made by any of the methods known in the art, e.g, by solution polymerization with free radical initiation, or by high pressure polymerization, conveniently carried out in autoclave or a tubular reactor.

Advantageously, polymerization is effected in the presence of an initiator and if desired or required a molecular weight regulator at elevated pressure, eg, between 90 and 125 bar (9 and 12.5 MPa) and elevated temperature, but preferably below about 130° C., for example within the range of from 90° C. to 125° C. Maintaining a temperature below the above-mentioned limit enables a polymer having the desired linearity to be obtained; other means of controlling linearity, as known in the art, may also be used.

The flow improver composition defined in the first aspect may advantageously also comprise an ethylene-unsaturated ester copolymer. As the unsaturated ester component there may be mentioned more especially a vinyl ester of a saturated carboxylic acid, or an ester of a saturated alcohol and an unsaturated carboxylic acid. The copolymer advantageously contains, in addition to units derived from ethylene, units of the formula

    --CH.sub.2 CR.sup.1 R.sup.9 --                             III

wherein R¹ has the meaning given above, and is advantageously hydrogen, and R⁹ represents a group of the formula COOR¹⁰ or OOCR¹⁰, wherein R¹⁰ represents a hydrocarbyl group.

The copolymer is advantageously ethylene-vinyl acetate or propionate copolymer, or an ethylene-acrylic ester copolymer. This copolymer may either be of the same type, (i) or (ii), as the terpolymer or of the other type. As disclosed in U.S. Pat. No. 3,961,916, flow improver compositions may comprise a wax growth arrestor and a nucleating agent. Without wishing to be bound by any theory, the applicants believe that if the terpolymer of the present invention is a type (i) copolymer, and has more than about 7.5 molar per cent of ester units, it acts primarily as an arrestor, and will benefit from the addition of a nucleator, e.g., an ethylene-vinyl ester, especially acetate, copolymer having a number average molecular weight in the range of 1200 to 20000, and a vinyl ester content of 0.3 to 17 molar per cent, advantageously an ester content lower, and preferably at least 2, more preferably at least 3, molar per cent lower, than that of the esters in the terpolymer composition.

If, however, the terpolymer of the invention is a type (ii) copolymer and contains less than about 10 molar per cent of ester units then correspondingly it acts primarily as a nucleator and will benefit from the presence of an arrestor which may be an ethylene/unsaturated ester copolymer with correspondingly lower molecular weight and higher ester content.

It has, however, unexpectedly been found that when the essential ethylene-unsaturated ester copolymer is of the same type as the terpolymer, further advantages in performance may result. Oil compositions according to the first aspect of the invention accordingly include those comprising the specified terpolymer in admixture with an ethylene-unsaturated ester, especially vinyl acetate or propionate copolymer of the same type, (i) or (ii), and in addition a further ethylene-unsaturated ester, especially a vinyl ester, copolymer of a different type, (i) or (ii). In this case, advantageously, the terpolymer and the copolymer, especially the acetate or propionate, copolymer will differ from the additional copolymer in molar ester proportion and number average molecular weight, the higher ester proportion preferably corresponding to the lower molecular weight. The ethylene/unsaturated ester, especially vinyl acetate or propionate, copolymer when present and the terpolymer are advantageously present in the composition in a weight ratio within the range of from 9:1 to 1:9, more advantageously in a ratio within the range of from 3:1 to 1:3, and preferably in a ratio of about 1:1.

The invention further provides, in a second aspect, an additive concentrate comprising the flow improver composition of the first aspect in admixture with an oil or a solvent miscible with oil.

The invention also provides, in a third aspect, the use of the flow improver composition of the first aspect to improve the low temperature properties of an oil, especially the CFPP of the oil, and the use of the above-defined concentrate to improve the same properties, the oil having at least 3% by weight of wax at 10° C. below cloud point.

In the oil-containing compositions of the invention, the oil may be a crude oil, i.e. oil obtained directly from drilling and before refining.

The oil may be a lubricating oil, which may be an animal, vegetable or mineral oil, such, for example, as petroleum oil fractions ranging from naphthas or spindle oil to SAE 30, 40 or 50 lubricating oil grades, castor oil, fish oils or oxidized mineral oil. Such an oil may contain additives depending on its intended use; examples are viscosity index improvers such as ethylene-propylene copolymers, succinic acid based dispersants, metal containing dispersant additives and zinc dialkyldithiophosphate antiwear additives. The terpolymer of this invention may be suitable for use in lubricating oils as a flow improver, pour point depressant or dewaxing aid.

The oil may be a fuel oil, e.g., a petroleum-based fuel oil, especially a middle distillate fuel oil. Such distillate fuel oils generally boil within the range of from 110° C. to 500° C., e.g. 150° C. to 400° C. The fuel oil may comprise atmospheric distillate or vacuum distillate, cracked gas oil, or a blend in any proportion of straight run and thermally and/or catalytically cracked distillates. The most common petroleum distillate fuels are kerosene, jet fuels, diesel fuels, heating oils and heavy fuel oils. The heating oil may be a straight atmospheric distillate, or it may contain minor amounts, e.g. up to 35 wt %, of vacuum gas oil or cracked gas oil or of both. The above-mentioned low temperature flow problem is most usually encountered with diesel fuels and with heating oils. The invention is also applicable to vegetable-based fuel oils, for example rape seed oil, used alone or in admixture with a petroleum distillate oil.

The terpolymer of the invention is useful in fuel oils having a relatively high wax content, such as a wax content above 3% by weight, measured at 10° C. below cloud point. Fuels in which the wax content is in the range of 3.3 to 6% by wt, especially 3.4 to 5% by wt at 10° C. below cloud point are especially suitable.

The terpolymer should preferably be soluble in the oil to the extent of at least 1000 ppm by weight per weight of oil at ambient temperature. However, at least some of the terpolymer may come out of solution near the cloud point of the oil and function to modify the wax crystals that form.

The additive concentrate, flow improver composition and oil composition may contain other additives for improving low temperature and/or other properties, many of which are in use in the art or known from the literature. These compositions may comprise additional cold flow improvers, including (A) a comb polymer.

Comb polymers (A) are polymers in which branches containing hydrocarbyl groups are pendant from a polymer backbone, and are discussed in "Comb-Like Polymers. Structure and Properties", N. A. Plate and V. P. Shibaev, J. Poly. Sci. Macromolecular Revs., 8, p 117 to 253 (1974).

Generally, comb polymers have one or more long chain hydrocarbyl branches, e.g., oxyhydrocarbyl branches, normally having from 10 to 30 carbon atoms, pendant from a polymer backbone, said branches being bonded directly or indirectly to the backbone. Examples of indirect bonding include bonding via interposed atoms or groups, which bonding can include covalent and/or electrovalent bonding such as in a salt.

Advantageously, the comb polymer is a homopolymer or a copolymer having, at least 25 and preferably at least 40, more preferably at least 50, molar per cent of the units of which have, side chains containing at least 6, and preferably at least 10, atoms.

As examples of preferred comb polymers there may be mentioned those of the general formula ##STR4## wherein D=R¹¹, COOR¹¹, OCOR¹¹, R¹² COOR¹¹, or OR¹¹,

E=H, CH₃, D, or R¹²,

G=H or D

J=H, R¹², R¹² COOR¹¹, or an aryl or heterocyclic group,

K=H, COOR¹², OCOR¹², OR¹² or COOH,

L=H, R¹², COOR¹², OCOR¹², COOH, or aryl,

R¹¹ ≧C₁₀ hydrocarbyl,

R¹² ≧C₁ hydrocarbyl or hydrocarbylene,

and m and n represent mole fractions, m being finite and preferably within the range of from 1.0 to 0.4, n being less than 1 and preferably in the range of from 0 to 0.6. R¹¹ advantageously represents a hydrocarbyl group with from 10 to 30 carbon atoms, while R¹² advantageously represents a hydrocarbyl or hydrocarbylene group with from 1 to 30 carbon atoms.

The comb polymer may contain units derived from other monomers if desired or required.

These comb polymers may be copolymers of maleic anhydride or fumaric or itaconic acids and another ethylenically unsaturated monomer, e.g., an α-olefin, including styrene, or an unsaturated ester, for example, vinyl acetate or homopolymer of fumaric or itaconic acids. It is preferred but not essential that equimolar amounts of the comonomers be used although molar proportions in the range of 2 to 1 and 1 to 2 are suitable. Examples of olefins that may be copolymerized with e.g., maleic anhydride, include 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene.

The acid or anhydride group of the comb polymer may be esterified by any suitable technique and although preferred it is not essential that the maleic anhydride or fumaric acid be at least 50% esterified. Examples of alcohols which may be used include n-decan-1-ol, ndodecan-1-ol, n-tetradecan-1-ol, n-hexadecan-1-ol, and noctadecan-1-ol. The alcohols may also include up to one methyl branch per chain, for example, 1-methylpentadecan-1-ol or 2-methyltridecan-1-ol. The alcohol may be a mixture of normal and single methyl branched alcohols. It is preferred to use pure alcohols rather than the commercially available alcohol mixtures but if mixtures are used the R¹² refers to the average number of carbon atoms in the alkyl group; if alcohols that contain a branch at the 1 or 2 positions are used R¹² refers to the straight chain backbone segment of the alcohol.

These comb polymers may especially be fumarate or itaconate polymers and copolymers such for example as those described in EP-A-153176, -153177 and -225688, and WO 91/16407.

Particularly preferred fumarate comb polymers are copolymers of alkyl fumarates and vinyl acetate, in which the alkyl groups have from 12 to 20 carbon atoms, more especially polymers in which the alkyl groups have 14 carbon atoms or in which the alkyl groups are a mixture of C₁₄ /C₁₆ alkyl groups, made, for example, by solution copolymerizing an equimolar mixture of fumaric acid and vinyl acetate and reacting the resulting copolymer with the alcohol or mixture of alcohols, which are preferably straight chain alcohols. When the mixture is used it is advantageously a 1:1 by weight mixture of normal C₁₄ and C₁₆ alcohols. Furthermore, mixtures of the C₁₄ ester with the mixed C₁₄ /C₁₆ ester may advantageously be used. In such mixtures, the ratio of C₁₄ to C₁₄ /C₁₆ is advantageously in the range of from 1:1 to 4:1, preferably 2:1 to 7:2, and most preferably about 3:1, by weight. The particularly preferred comb polymers are those having a number average molecular weight, as measured by vapour phase osmometry, of 1,000 to 100,000, more especially 1,000 to 30,000.

Other suitable comb polymers are the polymers and copolymers of α-olefins and esterified copolymers of styrene and maleic anhydride, and esterified copolymers of styrene and fumaric acid; mixtures of two or more comb polymers may be used in accordance with the invention and, as indicated above, such use may be advantageous. Other examples of comb polymers are hydrocarbon polymers, e.g., copolymers of ethylene and at least one α-olefin, the α-olefin preferably having at most 20 carbon atoms, examples being n-decene-1 and n-dodecene-1. Preferably, the number average molecular weight of such a copolymer is at least 30,000 measured by GPC. The hydrocarbon copolymers may be prepared by methods known in the art, for example using a Ziegler type catalyst.

Other additives for improving low temperature properties are:

(B) Polar nitrogen compounds.

Such compounds are oil-soluble polar nitrogen compounds carrying one or more, preferably two or more, substituents of the formula >NR¹³, where R¹³ represents a hydrocarbyl group containing 8 to 40 atoms, which substituent or one or more of which substituents may be in the form of a cation derived therefrom. The oil-soluble polar nitrogen compound is generally one capable of acting as a wax crystal growth inhibitor in fuels. It comprises for example one or more of the following compounds:

An amine salt and/or amide formed by reacting at least one molar proportion of a hydrocarbyl-substituted amine with a molar proportion of a hydrocarbyl acid having from 1 to 4 carboxylic acid groups or its anhydride, the substituent(s) of formula >NR¹³ being of the formula --NR¹³ R¹⁴ where R¹³ is defined as above and R¹⁴ represents hydrogen or R¹³, provided that R¹³ and R¹⁴ may be the same or different, said substituents constituting part of the amine salt and/or amide groups of the compound.

Ester/amides may be used, containing 30 to 300, preferably 50 to 150, total carbon atoms. These nitrogen compounds are described in U.S. Pat. No. 4,211,534. Suitable amines are predominantly C₁₂ to C₄₀ primary, secondary, tertiary or quaternary amines or mixtures thereof but shorter chain amines may be used provided the resulting nitrogen compound is oil soluble, normally containing about 30 to 300 total carbon atoms. The nitrogen compound preferably contains at least one straight chain C₈ to C₄₀, preferably C₁₄ to C₂₄, alkyl segment.

Suitable amines include primary, secondary, tertiary or quaternary, but are preferably secondary. Tertiary and quaternary amines only form amine salts. Examples of amines include tetradecylamine, cocoamine, and hydrogenated tallow amine. Examples of secondary amines include dioctacedyl amine and methylbehenyl amine.

Amine mixtures are also suitable such as those derived from natural materials. A preferred amine is a secondary hydrogenated tallow amine, the alkyl groups of which are derived from hydrogenated tallow fat composed of approximately 4% C₁₄, 31% C₁₆, and 59% C₁₈.

Examples of suitable carboxylic acids and their anhydrides for preparing the nitrogen compounds include ethylenediamine tetraacetic acid, and carboxylic acids based on cyclic skeletons, e.g., cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid and naphthalene dicarboxylic acid, and 1,4-dicarboxylic acids including dialkyl spirobislactones. Generally, these acids have about 5 to 13 carbon atoms in the cyclic moiety. Preferred acids useful in the present invention are benzene dicarboxylic acids e.g., phthalic acid, isophthalic acid, and terephthalic acid. Phthalic acid and its anhydride are particularly preferred. The particularly preferred compound is the amide-amine salt formed by reacting 1 molar portion of phthalic anhydride with 2 molar portions of dihydrogenated tallow amine. Another preferred compound is the diamide formed by dehydrating this amide-amine salt.

Other examples are long chain alkyl or alkylene substituted dicarboxylic acid derivatives such as amine salts of monoamides of substituted succinic acids, examples of which are known in the art and described in U.S. Pat. No. 4,147,520, for example. Suitable amines may be those described above.

Other examples are condensates, for example, those described in EP-A-327427.

(C) A compound containing a cyclic ring system carrying at least two substituents of the general formula below on the ring system

    --A--NR.sup.15 R.sup.16

where A is a linear or branched chain aliphatic hydrocarbylene group optionally interrupted by one or more hetero atoms, and R¹⁵ and R¹⁶ are the same or different and each is independently a hydrocarbyl group containing 9 to 40 atoms optionally interrupted by one or the substituents being the same or more hetero atoms, the substituents being the same or different and the compound optionally being in the form of a salt thereof. Advantageously, A has from 1 to 20 carbon atoms and is preferably a methylene or polymethylene group. Such compounds are described in WO 93/04148.

(D) A hydrocarbon polymer.

Examples of suitable hydrocarbon polymers are those of the general formula ##STR5## wherein T=H or R²¹ wherein

R²¹ =C₁ to C₄₀ hydrocarbyl, and

U=H, T, or aryl

and v and w represent mole fractions, v being within the being in the range of from range of from 1.0 to 0.0, w being in the range of from 0.0 to 1.0.

The hydrocarbon polymers may be made directly from monoethylenically unsaturated monomers or indirectly by hydrogenating polymers from polyunsaturated monomers, e.g., isoprene and butadiene.

Examples of hydrocarbon polymers are disclosed in WO 91/11488.

Preferred copolymers are ethylene a-olefin copolymers, having a number average molecular weight of at least 30,000. Preferably the α-olefin has at most 28 carbon atoms. Examples of such olefins are propylene, 1-butene, isobutene, n-octene-1, isooctene-1, n-decene-1, and n-dodecene-1. The copolymer may also comprise small amounts, e.g, up to 10% by weight, of other copolymerizable monomers, for example olefins other than a-olefins, and non-conjugated dienes. The preferred copolymer is an ethylene-propylene copolymer.

The number average molecular weight of the ethylene-α-olefin copolymer is, as indicated above, preferably at least 30,000, as measured by gel permeation chromatography (GPC) relative to polystyrene standards, advantageously at least 60,000 and preferably at least 80,000. Functionally no upper limit arises but difficulties of mixing result from increased viscosity at molecular weights above about 150,000, and preferred molecular weight ranges are from 60,000 and 80,000 to 120,000.

Advantageously, the copolymer has a molar ethylene content between 50 and 85 per cent. More advantageously, the ethylene content is within the range of from 57 to 80%, and preferably it is in the range from 58 to 73%; more preferably from 62 to 71%, and most preferably 65 to 70%.

Preferred ethylene-α-olefin copolymers are ethylenepropylene copolymers with a molar ethylene content of from 62 to 71% and a number average molecular weight in the range 60,000 to 120,000; especially preferred copolymers are ethylene-propylene copolymers with an ethylene content of from 62 to 71% and a molecular weight from 80,000 to 100,000.

The copolymers may be prepared by any of the methods known in the art, for example using a Ziegler type catalyst. The polymers should be substantially amorphous, since highly crystalline polymers are relatively insoluble in fuel oil at low temperatures.

Other suitable hydrocarbon polymers include a low molecular weight ethylene-α-olefin copolymer, advantageously with a number average molecular weight of at most 7500, advantageously from. 1,000 to 6,000, and as measured by vapour preferably from 2,000 to 5,000, as measured by vapour phase osmometry. Appropriate α-olefins are as given above, or styrene, with propylene again being preferred. Advantageously the ethylene content is from 60 to 77 molar per cent, although for ethylene-propylene copolymers up to 86 molar per cent by weight ethylene may be employed with advantage.

(E) A polyoxyalkylene compound. Examples are polyoxyalkylene esters, ethers, ester/ethers and mixtures thereof, particularly those containing at least one, preferably at least two, C₁₀ to C₃₀ linear alkyl groups and a polyoxyalkylene glycol group of molecular weight up to 5,000, preferably 200 to 5,000, the alkyl group in said polyoxyalkylene glycol containing from 1 to 4 carbon atoms. These materials form the subject of EP-A-0 061 895. Other such additives are described in U.S. Pat. No. 4,491,455.

The preferred esters, ethers or ester/ethers are those of the general formula

    R.sup.31 --O(D)--O--R.sup.32

where R³¹ and R³² may be the same or different and represent

(a) n-alkyl-

(b) n-alkyl-CO--

(c) n-alkyl-O--CO(CH₂)_(x) -- or

(d) n-alkyl-O--CO(CH₂)_(x) --CO--

x being, for example, 1 to 30, the alkyl group being linear and containing from 10 to 30 carbon atoms, and D representing the polyalkylene segment of the glycol in which the alkylene group has 1 to 4 carbon atoms, such as a polyoxymethylene, polyoxyethylene or polyoxytrimethylene moiety which is substantially linear; some degree of branching with lower alkyl side chains (such as in polyoxypropylene glycol) may be present but it is preferred that the glycol is substantially linear. D may also contain nitrogen.

Examples of suitable glycols are substantially linear polyethylene glycols (PEG) and polypropylene glycols (PPG) having a molecular weight of from 100 to 5,000, preferably from 200 to 2,000. Esters are preferred and fatty acids containing from 10-30 carbon atoms are useful for reacting with the glycols to form the ester additives, it being preferred to use a C₁₈ -C₂₄ fatty acid, especially behenic acid. The esters may also be prepared by esterifying polyethoxylated fatty acids or polyethoxylated alcohols.

Polyoxyalkylene diesters, diethers, ether/esters and mixtures thereof are suitable as additives, diesters being preferred for use in narrow boiling distillates, when minor amounts of monoethers and monoesters (which are often formed in the manufacturing process) may also be present. It is preferred that a major amount of the dialkyl compound be present. In particular, stearic or behenic diesters of polyethylene glycol, polypropylene glycol or polyethylene/polypropylene glycol mixtures are preferred.

Other examples of polyoxyalkylene compounds are those described in Japanese Patent Publication Nos. 2-51477 and 3-34790, and the esterified alkoxylated amines described in EP-A-117,108 and EP-A-326,356.

It is within the scope of the invention to use two or more additional flow improvers advantageously selected from one or more of the different classes outlined above.

The additional flow improver is advantageously employed in a proportion within the range of from 0.01% to 1%, advantageously 0.05% to 0.5%, and preferably from 0.075 to 0.25%, by weight, based on the weight of fuel.

The flow improver composition of the invention may also be used in combination with one or more other co-additives such as known in the art, for example the following: detergents, particulate emission inhibitors, storage stabilizers, antioxidants, corrosion inhibitors, dehazers, demulsifiers, antifoaming agents, cetane improvers, cosolvents, package compatibilizers, and lubricity additives.

The oil, especially fuel oil, composition of the invention advantageously contains the terpolymer of the invention in a proportion of 0.0005% to 1%, advantageously 0.001 to 0.1%, and preferably 0.02 to 0.06% by weight, based on the weight of fuel. In the high wax fuel to which the present invention is especially applicable the proportion is advantageously from 0.025 to 0.2%, preferably about 0.04%, by weight, based on the weight of the fuel.

Additive concentrates according to the invention advantageously contain between 3 and 75%, preferably between 10 and 65%, of the composition or terpolymer in an oil or a solvent miscible with oil.

The following Examples, in which all parts and percentages are by weight, and number average molecular weights (Mn) are measured by gel permeation chromatography with polystyrene as standard, illustrate the invention.

EXAMPLES 1 TO 4 Preparation of Terpolymer Example 1

An autoclave was charged with 782 ml (610 g) cyclohexane, 190 ml (168 g) vinyl octanoate (VnO) and 10 ml (9 g) vinyl acetate (VAC). The vessel was pressurized to 9.7 MPa with ethylene and the temperature of the solution raised to 123° C., this pressure and temperature being maintained throughout the reaction. A mixture of 453 ml vinyl octanoate and 24 ml vinyl acetate was injected into the autoclave over 75 minutes, as were 9.1 ml t-butyl per-2-ethyihexanoate dissolved in 58.2 ml cyclohexane. The vessel was heat soaked for 10 minutes at 123° C. at the end of the injection, and the reaction mixture drained from the autoclave. Unreacted monomers and solvents were removed by vacuum distillation, and 450 g of opaque, viscous polymer recovered.

Further terpolymers were prepared according to the general procedure given above, the proportions of monomers being varied to give polymers also as set out in the Table. The terpolymer may contain some residual monomer.

                  TABLE 1                                                          ______________________________________                                         Example CH.sub.3 /100 CH.sub.2                                                                    Mn      VnO mole %                                                                             VAC mole %                                  ______________________________________                                         1       5.0*       --      13.3    1.8                                         2       5.2*       --      14.6    1.7                                         3       5.0*       --      14.2    1.7                                         4       2.91       3865    14.0    1.54                                        ______________________________________                                          *not corrected for terminal methyl groups.                                     -- not measured.                                                         

COMPARISON EXAMPLES 1 TO 4

In these examples, ethylene-vinyl octanoate, ethylene-vinyl-2-ethylhexanoate, and ethylene-vinyl acetate-vinyl-2-ethylhexanoate copolymers were prepared using reaction conditions as described for Example 1, and in Table 2 below.

                  TABLE 2                                                          ______________________________________                                         Example                                                                               Temp., ° C.                                                                       CH.sub.3 /100 CH.sub.2                                                                    Mn   VnO  VAC  V2EH                                ______________________________________                                         Comp 1 123       2.8        4950 --   --   11.7                                Comp 2 123       4.6        3510 12.6 --   --                                  Comp 3 115       4.0        4030 --   1.2  12.8                                ______________________________________                                    

In addition, for comparison purposes, a commercially available ethylene-vinyl acetate, with about 11.9 mole % VA, Mn 3000, CH₃ /100 CH₂ 3.3, was used as Comp. 4.

In the Examples below, fuels having the characteristics given in Table 3 below were employed. The CFPP of the fuels is measured as described in "Journal of the Institute of Petroleum", 52 (1966), 173.

                  TABLE 3                                                          ______________________________________                                                               Fuel 1                                                                               Fuel 2                                             ______________________________________                                         Cloud Point, ° C.                                                                               -6      -3                                             CFPP, ° C.       -8      -4                                             IBP, ° C.        154     174                                            FBP, ° C.        361     369                                            90-20° C.        80      110                                            FBP-90° C.       31      26                                             Wax Content at 10° C. below Cloud Point, wt %                                                   3.4     2                                              ______________________________________                                    

EXAMPLE 5 AND COMP. EXAMPLE 5 Tests on Oil Compositions--Effect on CFPP

In these Examples, the CFPP of an oil composition according to the first aspect of the invention is examined.

The oil composition of Example 5 contained the terpolymer of Example 4. Comp. Example 5 contained an ethylene-vinyl acetate copolymer (Comp. 4) as the flow improver composition. The additives were used at a total treat rate of active ingredients as shown, e.g., if treat rate is shown as 100 ppm the additive is present at a treat rate of 100 ppm active ingredient.

The results are set out in Table 4 below. Each result is the average of at least two experiments.

                  TABLE 4                                                          ______________________________________                                                                 CFPP, ° C.                                                              Fuel                                                                         Terpolymer  1    2                                       Treat Rate, ppm                                                                             Example  of Example  400  100                                     ______________________________________                                                    --     --          -8     -4                                                   5      4           -17    -5                                                   Comp 5 Comp 4      -11    -16.5                                     ______________________________________                                    

The results show the effectiveness of the terpolymer alone in the higher wax fuel 1 and its relative ineffectiveness in the lower wax fuel 2. 

What is claimed is:
 1. A fuel oil composition comprising a fuel oil having a wax content of 3.3 to 6% by weight at 10° C. below its cloud point, and 0.025 to 0.2% by weight, based on the weight of fuel oil, of a flow improver composition comprising an oil-soluble ethylene terpolymer having, in addition to units derived from ethylene, units of the formula: ##STR6## and units of the formula ##STR7## wherein R¹ and R², which may be the same or different, each represent H or methyl, R³ represents an alkyl group having up to 4 carbon atoms, and R⁴ represents n-heptyl; the degree of branching of the terpolymer, as measured by proton NMR spectroscopy being less than 6 CH₃ groups per 100 CH₂ units.
 2. A composition as claimed in claim 1, wherein R¹ and R² each represent hydrogen and R³ represents methyl.
 3. A composition as claimed in claim 1, wherein the terpolymer has a number average molecular weight (Mn), measured by gel permeation chromatography, of at most 20,000.
 4. A composition as claimed in claim 1, wherein a total molar proportion of units I and II is within the range of from 10 to 25 percent, and Mn is within the range of from 3,000 to 6,000.
 5. A composition as claimed in claim 1, wherein the total molar proportion of units I and II is within the range of from 3.5 to 7 molar percent, and Mn is within the range of from 3,000 to 10,000.
 6. A composition as claimed in claim 1, wherein the flow improver composition also comprises an ethylene-unsaturated ester copolymer.
 7. A method of improving the low temperature flow properties of a fuel oil having a wax content of from 3.3 to 6% by weight at 10° C. below its cloud point, the method comprising adding to said fuel oil 0.025 to 0.2% by weight, based on the weight of fuel oil, of an oil-soluble ethylene terpolymer having, in addition to units derived from ethylene, units of the formula: ##STR8## and units of the formula ##STR9## wherein R¹ and R², which may be the same or different, each represent H or methyl, R³ represents an alkyl group having up to 4 carbon atoms, and R⁴ represents n-heptyl; the degree of branching of the terpolymer, as measured by proton NMR spectroscopy being less than 6 CH₃ groups per 100 CH₂ units.
 8. A method as claimed in claim 7 wherein R¹ and R² each represent hydrogen and R³ represents methyl.
 9. A method as claimed in claim 7 wherein the terpolymer has a number average molecular weight (M_(n)), measured by gel permeation chromatography, of at most 20,000.
 10. A method as claimed in claim 7 wherein the total molar proportion of units I and II is within the range of from between 10 to 25 percent, and M_(n) is within the range of from between 3,000 to 6,000.
 11. A method as claimed in claim 7 wherein the total molar proportion of units I and II is within the range of from between 3.5 to 7 molar percent, and M_(n) is within the range of from between about 3,000 to 10,000.
 12. A method as claimed in claim 7 wherein there is also added an ethylene-unsaturated ester coploymer.
 13. A fuel oil composition as claimed in claim 1, wherein the fuel oil has a wax content of 3.4 to 5% by weight at 10° C. below its cloud point.
 14. A method as claimed in claim 7, wherein the fuel oil has a wax content of 3.4 to 5% by weight at 10° C. below its cloud point. 